| 摘要 |
A CPU unit 2 has a liquid crystal display screen 10 , a plurality of operation keys 12 , and the like. Each of expansion units 3 to 8 has a push switch button 14 . For example, when an operator pushes the switch button 14 - 1 of the ID- 1 unit 3 , information concerning the unit 3 is displayed on the liquid crystal screen 10 . Next, the operator operates one of the predetermined operation keys 12 of the CPU unit 2 , whereby the display contents of the screen 10 are removed and another piece of information concerning the unit 3 is displayed.
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